digital compass modules

[Christopher Heiny]

On Wednesday 23 January 2008, ground control picked up the following 
transmission from luc at bos-boon.nl:
> Citeren Schmidt András <asch at freemail.hu>:
> >   1. The map of a GPS map viewer application turns when you turn
> > the machine so it is always aligned with the environment (this
> > feature is included on some GPS tools.)
>
> A handheld GPS use the change in position measured by GPS to  
> determinate the direction of movement and is able to turn the display
>   in that direction.
>
> In fact, when the GPS is working like it should (IE very good with
> the   planned chipset) this is the best way to calculate the heading.
>
> Most important: it's already there in the phone.

Use case: I'm hiking in the mountains, heading 0 degrees (due north) at 
5 km/h.  I stop because there's something interesting off to the left, 
and I want to get its exact bearing (let's assume that's something like 
283 degrees).  So I rotate the GPS so "up" points at the object of 
interest.

Results: Handheld with internal compass (for example, many Garmin units) 
can give me correct bearing to the object.  Neo thinks bearing to the 
object is 0 degrees, since I'm not moving and you can't compute 
rotation about axis with GPS signal only.

Failure mode: Stationary GPS is more subject to false readings due to 
reflection than moving GPS.  Due to reflections, Neo might think I'm 
moving in some random direction, and give a bogus heading that appears 
reliable.